Electronic switch display in chopped operation of oscilloscopes



Sept. 29, 1964 M. MARON ELECTRONIC SWITCH DISPLAY IN CHOPPED OPERATIONOF OSCILLOSCOPES Filed Jan. 51, 1961 9m omm mwoml mwmim 1 En ENVENTORMeyer Moron -g aflgd-o a'fi ATTOR'NIEIYS United States Patent ELECTRON CSWITCH DISPLAY 1N (SHOkPED OPERATlON OF OSfiiLLOSCOPES Meyer Maren, EastPaterson, N..l., assignor to Fairchild Qamera and instrumentCorporation, Syosset, N.Y., a corporation of Delaware Filed Jan. 31,1901, Ser. No. 86,071

'7 Claims. (til. 315-23) This invention is directed to chopped orrapidly switched operation of time sharing oscilloscopes arranged toview two independent displays on the same viewing screen. When one ofthe displays is at a very low frequency the usual alternatepresentations of the two displays by time sharing switches is apt tocause flicker in the presentations. This is particularly objectionablewhen one of the displays is an electrical wave which requires anappreciable fraction of a second for its completion, and when the otherdisplay is a dot presentation for direct readout measurement of theelectrical Wave, as described in a copending application by Bernard L.Hegeman, entitled Direct Readout System for Oscilloscopes, Serial No.34,124, filed June 6, 1960.

Chopped operation is not new as regards oscilloscopes equipped with timesharing electronic switches for a single electron beam. It has beenusual in such operation to provide a free running multivibrator togenerate substantially rectangular or square waves for operation of theelectronic switches at a relatively high frequency, say at severalthousand cycles. Separation of two independent displays may be providedas described in a copending patent application by Fred L. Katzmann,entitled Time Sharing Oscilloscope, Serial No. 55,014, assigned to thesame assignee as the instant application.

In chopped operation the high frequency electronic switches alternatelypresent small portions of each of the independent displays at twoseparated positions on the viewing screen. One defect in such a choppingoperation has been the appearance of switching excursion transientsbetween the separated waves. When the chopping frequency is very highrelative to the frequency of the displayed waves, the displays may beconsidered as being made up of a great number of alternately presenteddots which blend into two apparently continuous traces, one of each ofthe separated displays. As the beam switches back and forth between thetwo displays a great number of faint vertical lines appears on thedisplay screen between the two separated traces. These are caused by theswitching excursion transients of the beam as it shuttles rapidlyback'and forth between the separated displays.

The defect in appearance of the display is due to a faint but apparentsmear between the displays. My invention avoids this defect of smearingbetween the separate displays without the use of blanking signalsderived (by costly circuits) from the switching wave transientsthemselves.

It is, therefore, an object of my invention to provide simplifiedcircuitry for chopped operation of an oscilloscope in which twoseparated independent displays appear clearly and sharply against auniform dark background.

It is another object of my invention to derive a high frequencyelectronic switching wave from a blanking wave so that the switchingexcursion transients occur within the blanking interval.

It is still another object of my invention to prevent a smeared displaybetween two independent displays produced by chopped operation.

It is a still further object of my invention to provide direct readoutdots for quantitative measurements without objectionable flicker orsmear when measuring a low frequency display.

Other objects will be understood by those skilled in the art afterconsideration of the description and annexed drawings, in which,

FIGURE 1 illustrates a prior art presentation of two separatedindependent displays in chopped operation;

FIGURE 2 illustrates a presentation according to this invention; and

FIGURE 3 is a schematic circuit of a preferred embodiment of thisinvention.

Referring to FIGURE 1, a prior art display screen is depicted in whichtwo independent displays 101, 102 are shown in separated relationship,as normally produced by the technique well known as chopping. Segments104, of each display are produced by switching alternately from onedisplay to the other at a high rate. Switching excursion transients 103occur on each switching operation between display portions such as 104to 106 and 106 to 108. Thus, switching results in a shaded or smearedarea between the displays.

In FIGURE 2 the same two displays 101, 102 are depicted according to myinvention as they appear on a display screen 200 with a uniformly dark(unshaded) background 203. Elimination of the prior art transients 103is achieved by the circuitry shown in FIGURE 3.

In this preferred embodiment of my circuit, electronic switch 330 hastwo pairs of push-pull input terminals 301, 303 and 302, 304 to whichdisplay waves 101 and 102 are applied, respectively. Out-of-phaseswitching waves 321, 322 are generated at a high frequency j (which maybe, for example, 100,000 cycles per second), in a well known bistableinultivibrator circuit 340.

These switching waves are applied through diodes 307, 308 to thecathodes of push-pull pairs of tubes 305, 306, respectively, to makethem alternately conductive. Thus, when a portion 104 of potential wave101 is amplified by 305 and applied to the input conductors 318 and 319of the vertical paraphase amplifier 317, a synchronous correspondingportion 105 of wave 102 is cut off and does not appear at the input to317. Immediately succeeding portions of 101, 102, such as 104, 106, areamplified alternately in 317 and applied to the vertical deflectingplates V, V'. A portion of switch waves 321, 322 is applied to grids310, 311 of trace separator tubes 309.

Thus, when the negative excursion of switch wave 321 switches displaywave 101 to the plates V, V input conductor 318 is positive with respectto 319 and V is positive with respect to V. This will produce display101 near the top of display screen 200. Similarly, display 102 will beproduced near the bottom of 200, and the two are separated. The amountof separation is adjustable by means of potentiometer unicontrol 315.

The multivibrator 350 is arranged to generate a narrow negative pulsewave 320 at a free running frequency of 2 f which may be, for example,200,000 cycles per second. The duration t of a pulse 370 is madeslightly longer than the time required for the switching transient 103of square waves 321 and 322. The wave 320 is used to start the switchingaction of the flip-flop generator 340 by means of a capacitor 314connected to the junction of the cathodes of diodes 312 and 313. Forexample, t is made equal to 1.5 microseconds when 103 endures for only1.3 microseconds, that is, t begins with the switching action and beforeswitching is complete and ends after the switching is completed.

The output wave 320 serves two purposes: to synchronize the switch wavegenerator 340, and to blank out the switching transients which occur dueto chopped operation. In order to accomplish this latter result, theblanking wave 320 is applied to the control grid 325 of cathode ray tube331, through the blanking pulse diode 328 and cathode follower 329. Abrightening pulse diode 326 may be used to control the intensity of beam323 between the blanking pulses 320 by means of the brights3 nessadjusting potentiometer 327 which controls the positive potential on thegrid of cathode follower 329, and thus the value of potential applied tothe intensity control grid 325. Horizontal sweep waves are applied tothe H-deflection plates H and H in any conventional manner, as from asweep generator 316.

A low cost circuit has been described which utilizes a free runningmultivibrator 350 to synchronize the switch wave generator 346 and atthe same time to turn off the electron beam 323 during the switchingoperation.

This low cost circuit is extremely useful in an oscilloscope adapted fordirect readout measurements using dot producing waves alternately with adisplay wave as described in the copending Hegeman application abovementioned.

When two completely independent displays, such as an electrical waveformand readout dots for measuring this waveform, are presented alternatelyat a very low frequency of a few cycles per second or a fraction of acycle per second, chopped operation is desirable to prevent a slowblinking of the dots and flicker of the waveform.

Normally, when chopped operation of such low frequency displays isutilized, the double switching transients which occur between thedisplayed waveform and the dots, due to rapid switching in both thevertical and horizontal dimensions, produce fan-shaped hazy areascentered on each dot and extending to all parts of the displayedwaveform. In fact, the background of the entire pattern being displayedhas so much unwanted transient hash extending in all directions that thedots are practically useless for the purpose of reading out quantitativeinformation about the waveform.

By the use of my invention the dots and the displayed waveform appear onthe displayed pattern with sharp, clean separation. In this case, the Hsweep generator 316 will include a high frequency switch such as the Hswitch 350 of FIGURE 3 of the Hegeman application.

The switching terminals 380, 331 of generator 316 are supplied withwaves 321, 322 respectively, and the terminals 382, 383 are suppliedwith calibrating wave 162 in order to switch the time base sweep wave390 to plates H and H simultaneously as the displayed waveform 101 isswitched to V and V, and to switch a dot producing sweep wave 102 (whichis the rectangular calibrating wave) to H and H when it is switched to Vand V' by the vertical switch 330. Thus, both the display and sweepwaves are presented alternately in rapid, chopped operation to preventflicker of the display or blinking of the dots in presentations of lowfrequency waveforms.

While I have described a preferred form of my invention and havedescribed it in its application to the chopped display of two separatewaveforms as well as to the chopped display of a single waveformtogether with calibrating index and readout dots therefor, it will beunderstood that other forms of the invention may be devised and otherapplications for the invention are entirely possible. Therefore, I wishto be limited not by the foregoing specification, but, on the contrary,solely by the claims granted to me.

What is claimed is:

1. In an oscilloscope having a cathode ray tube with a single electronbeam and a fluorescent screen, means for presenting two electricalwaveforms on separate portions of the tube screen comprising, incombination, means to deflect the electron beam in a first dimension toprovide a time base for the waveforms, means to deflect the electronbeam in a second dimension in accordance with the waveforms, means forgenerating a switching wave, means for controlling said second electronbeam deflecting means to separate the waveform displays, means forapplying said generated switching waves to said controlling means toposition said beam in said separate tube screen portions alternately,said last-named means including means for combining each electricalwaveform with a portion of said switch wave and means to cut off theelectron beam during transition periods of said switching means tothereby assure that there will be no trace extending from one of saidseparated displays to the other.

2. In an oscilloscope having a cathode ray tube with a single electronbeam and a fluorescent screen, means for presenting two electricalwaveforms on separate portions of the tube screen comprising, incombination, means to deflect the electron beam in a first dimension toprovide a time base for the waveforms, means to deflect the electronbeam in a second dimension in accordance with the waveforms, means togenerate blanking pulses, means for generating a switching wave, meansfor controlling said second electron beam deflecting means to separatethe waveform displays, and means for applying said generated switchingwaves to said controlling means to position said beam in said separatedtube screen portions alternately, said last-named means including meansfor combining each electrical waveform with a portion of said switchwave, said blanking pulses initiating operation of said switching means,said blanking pulses also cutting off the electron beam duringtransition periods of said switching means to thereby assure that therewill be no trace extending from one of said separated displays to theother.

3. In an oscilloscope having a cathode ray tube with a single electronbeam and a fluorescent screen, means for presenting two electricalwaveforms on separate portions of the tube screen comprising, incombination, means to deflect the electron beam in a first dimension toprovide a time base for the waveforms, said time base deflectionrecurring at a predetermined frequency, means to deflect the electronbeam in a second dimension in accordance with the waveforms, means forgenerating a switching wave having a frequency greater than said timebase recurrence frequency, means for controlling said second electronbeam deflecting means to separate the waveform displays, means forapplying said generated switching wave to said controlling means toposition said beam in said separate tube screen portions alternately,said last-named means including means for combining each electricalwaveform with a portion of said switch wave and means to cut off theelectron beam during transition periods of said switching means tothereby assure that there will be no trace extending from one of saidseparated displays to the other.

4. In an oscilloscope having a cathode ray tube with a single electronbeam and a fluorescent screen, means for presenting two electricalwaveforms on separate portions of the tube screen comprising, incombination, means to deflect the electron beam in a first dimension, toprovide a time base for the waveforms having a pre determined frequencyof recurrence, means to deflect the beam in a second dimension inaccordance with the waveforms, bistable means responsive to pulses forgenerating a square switching wave, said bistable means having apredetermined opera-ting time, means to generate pulses of a durationslightly greater than said operating time, said pulses recurring at afrequency greater than the frequency of recurrence of said time base,means applying said pulses to said bistable square-Wave switching meansfor controlling said first electron beam deflecting means to separatethe waveform displays, means for applying said square switching wave tosaid controlling means to position the electron beam in said separatetube screw portions alternately, said last-named means including meansfor combining each electrical waveform with a portion of said switchwave, and means to cut off the electron beam during operating times ofsaid bistable means.

5. In a cathode ray oscilloscope having a cathode ray tube including afluorescent screen, a single electron beam source and two deflectionmeans for deflecting said electron beam across said screen in twodirections; in combination; means for applying an electrical waveform tobe analyzed to one deflection means and for simul- :5 taneously applyinga second electrical timing wave to the other deflection means; means toproduce a pair of phase related rectangular electrical Waves of the samefrequency relative to one another; means to apply said rectangularelectrical Waves one to each of said deflection means simultaneously;and electronic switching means for alternately applying portions of saidelectrical waveform and said timing wave and portions of said pairs ofrectangular waves to said one deflection means whereby portions of aWaveform to be analyzed are displayed alternately on said screen with atleast one of a pair of dots.

6. In a cathode ray oscilloscope having a cathode ray tube including afluorescent screen, a single electron beam source and two deflectionmeans for deflecting said electron beam across said screen in twodirections; in combination; means for applying an electrical Waveform tobe analyzed to one deflection means and for simultaneously applying asecond electrical timing wave to the other deflection means; means toproduce a pair of phase related rectangular electrical waves one to eachof said deflection means simultaneously; means to control the intensityof the electron beam; means to apply a blanking signal of short durationand of much higher frequency than said rectangular waves to saidintensity control means; means to generate a switching wave from saidblanking signal, with switching transients synchronous with and shorterthan said blanking duration; and electronic switching means operated bysaid switching wave for alternately applying portions of said electricalwaveform and said timing wave and portions of said pairs of rectangularwaves to said one deflection means whereby portions of a waveform to beanalyzed are displayed *3 alternately on said screen with at least oneof a pair of dots against a dark background.

7. In a cathode ray oscilloscope having a cathode ray tube including afluorescent screen, a single electron beam source and two deflectionmeans for deflecting said electron beam across said screen in twodirections; in combination; means for applying a low frequencyelectrical Waveform to be analyzed to one deflection means and forsimultaneously applying a second electrical timing Wave synchronized bysaid electrical waveform to the other deflection means; means to producea pair of phase related rectangular electrical waves of the samefrequency relative to one another and of higher frequency than saidtiming wave; means to apply said rectangular electrical waves one toeach of said deflection means simultaneously; means to control theintensity of the electron beam; means to apply a blanking signal ofshort duration and of much higher frequency than said rectangular wavesto said intensity control; means to generate a switching Wave from saidblanking signal, with switching transients synchronous with and shorterthan said blanking duration; and electronic switching means operated bysaid switching wave for alternately applying portions of said electricalwaveform and said timing wave and portions of said pairs of rectangularwaves to said one deflection means whereby portions of a waveform to beanalyzed are displayed alternately on said screen with at least one of apair of dots against a dark background.

References Cited in the file of this patent UNITED STATES PATENTS2,706,265 Buehler Apr. 12, 1955 2,858,475 Blake Oct. 28, 1958 2,997,620Katzmann Aug. 22, 1961

1. IN AN OSCILLOSCOPE HAVING A CATHODE RAY TUBE WITH A SINGLE ELECTRONBEAM AND A FLUORESCENT SCREEN, MEANS FOR PRESENTING TWO ELECTRICALWAVEFORMS ON SEPARATE PORTIONS OF THE TUBE SCREEN COMPRISING, INCOMBINATION, MEANS TO DEFLECT THE ELECTRON BEAM IN A FIRST DIMENSION TOPROVIDE A TIME BASE FOR THE WAVEFORMS, MEANS TO DEFLECT THE ELECTRONBEAM IN A SECOND DIMENSION IN ACCORDANCE WITH THE WAVEFORMS, MEANS FORGENERATING A SWITCHING WAVE, MEANS FOR CONTROLLING SAID SECOND ELECTRONBEAM DEFLECTING MEANS TO SEPARATE THE WAVEFORM DISPLAYS, MEANS FORAPPLYING SAID GENERATED SWITCHING WAVES TO SAID CONTROLLING MEANS TOPOSITION SAID BEAM IN SAID SEPARATE TUBE SCREEN PORTIONS ALTERNATELY,SAID LAST-NAMED